As a string, just use FormatDecimal, e.g.
FormatDecimal(5.96000003814967, 5) results in the string "5.96000"
If you need to keep a number, multiply by 10^number_of_decimals, floor() it and divide again by 10^number_of_decimals, e.g.
floor(5.96000003814967 * 100) / 100 results in the number 5.96
I answer just because it was a wonderful sunny day with a clear blue sky (the first since almost 4 months), which gave me some extra energy.